Samaas is a term used in Hindi grammar. Its meaning is to abbreviate two or three words, such as if we have to say "Rasoee Ke Liye Ghar", we can tell this long phrase combining them as "Rasoee Ghar".

This combination is not according to Samaas rules, but when a word is formed by Samaas rules it is called Samaasik word. In this process the marks of dividing a word get disappeared, eg Raajputra. Thus in any Samaas word has two words - the first word is called Poorv Pad and the latter word is called Uttar Pad. When this compound word is analyzed to clear the Samaas it is called Samaas Vigraha. In the above example Raaj is Poorv Pad and Putra is Uttar Pad. Gangaajal is another example. In this word Gangaa is Poorv Pad and Jal is Uttar Pad.

In this process two words are combined to make a third word which is complete in its meaning. Samaas has no definite rule of making Samaas, but when the second word starts with a consonant, then only a Samaas is formed, for example Udyog + Pati = Udyogpati; or Asht + Bhujaa = Ashtbhujaa. Here the second word is started with a consonant, while the first word may have started with a vowel --

Types of Samaas
With this process Samaas are of 4 types -

(1) Avyayee Bhaav Samaas
eg Aa+Maran = Aamaran. In this type of compound word when the first Pad (Poorv Pad) is more important than the second or latter (Uttar) Pad and is Avyaya, it is called Avyayee Bhaav Samaas, such as
Aa-Jeevan = whole life
Yathaa-Shakti = According to one's strength
Har+Roz = Roz Roz = everyday
Raaton-Raat = Ek Raat mein = in one night only
Prati+Din = Pratidin = everyday

In this Samaas the whole word becomes Avyaya and its form does not change and there is no mark of any kind of division as given in above examples.

(2) Tatpurush Samaas
eg Mahaa+raaj = Mahaaraaj. In whichever Samaas the Uttar Pad (latter word) is main and the Poorv Pad (first word) is secondary that is called Tatpurush Samaas, for example Tuasee+daas+krit = Tulasee Daas Krit (means Tulasee Daas created)

Tatpurush Samaas is of 3 types -
--Natra Tatpurush Samaas - in whichever complete word the first word is negative, it is called Natra Samaas, eg A-Samaya, A-Sabhya, An-Ant, Nir-Vikaar
--Karm Dhaaraya Samaas - In whichever complete word the first word is main or adjective and the second word is qualified by the first word, it is called Karm Dhaaraya Samaas, eg Chandra+mukh = who has a face like Chandra, Deh+lataa = Whose body is like creeper, Neel+Kamal = Kamal which is blue; Saj+Jan = Who is good Jan (man)
--Dwigu Samaas - In whichever complete word the first word is numerical adjective and the second word is a simple noun is called Dwigu Samaas, eg Nava-Graha, Tri-Lok, Do-Pahar, Chau-Maasaa

(3) Dwandwa Samaas
In which ever complete word both words are of equal status and if they are analyzed the both words are joined by "and" or "Or" eg Raam+Krishn = Raam and Krishn, Paap-Punya = Paap and Punya, Seetaa-Raaam - Seetaa and Raam, Oonch-Neech - Oonchaa or Neechaa; that is called Dwandwa Samaas.

(4) Bahubreehi Samaas
Whichever complete word has its both the words secondary and the complete word's meaning has no relationship with the meanings of its both the words' meanings, that is called Bahubreehi Samaas, eg Neel+Kanth = Neelkanth = Shiv Jee. Here neither Neel (blue), nor Kanth (throat) has any relationship with Shiv. In the same way ---
Dashaanan = who has ten heads = Raavan,
Su+lochanaa = who has beautiful eyes = wife of Meghnaad,
Megh+Naad = who made noise like clouds = Raavan's son
Lambo-dar = whose stomach is large = Ganesh Jee

Difference Between Sandhi (joining) and Samaas
Sandhi is among alphabets and in this Vibhakti or a word does not disappear, eg Dev-aalaya = Devaalaya
Samaas is between two words and in this Vibhakti or a word may disappear too, eg MaataPitaa = Maataa and Pitaa

Difference Between Karmdhaaraya and Bahubreehi Samaas
In Karmdhaaraya Samaas, the whole word is the adjective of the other word, and in this the meaning of the whole word is main, eg Neel+Kanth.
In Bahubreehi Samaas, relationship of both the words is not as a qualifier and qualifying, but the whole word is the qualifier of some other noun etc word. Meaning of the complete word is secondary, and some other meaning of that complete word becomes main, eg Neel+Kanth = whose throat is blue = Shiv Jee

Vibhakti
(1) Karm, (2) Karan, (3) Sampradaan, (4) Apaadaan (5) Sambandh, (6) Adhikaran,

Kartaa, Karm, Karan, Upaadaan