What this suffix does
The suffix -hood creates nouns that name stages of life, human states or conditions, and in some cases communities or groups. From "child" you get "childhood"; from "adult" you get "adulthood"; from "neighbor" you get "neighborhood".
Unlike -ness or -tion, -hood is not freely productive: you cannot add it to any word. There is a fixed set of -hood words that should be learned as established vocabulary.
The main uses of -hood
Three clear groups:
1. Life stages: childhood, adulthood, manhood, womanhood, parenthood, boyhood, girlhood.
2. States or conditions: falsehood, likelihood, brotherhood, sisterhood.
3. Communities or roles: neighborhood, priesthood, knighthood.
In everyday speech, the most frequent ones are childhood, adulthood, neighborhood and parenthood.
Do not confuse -hood with the noun "hood"
The word "hood" in English literally means a covering for the head, or informally "neighbourhood" (from hip-hop culture).
The suffix -hood has nothing to do with a physical hood: it comes from Old English and means "state" or "condition". It is a historical coincidence that the free word and the suffix look identical.