The term PRESSURE SOURCE can be broken down into two crossword solutions: PEER (4 letters) and PEERS (5 letters). PEER is a noun that refers to a person of the same age, status, or ability. PEERS is a plural form of the same word, referring to more than one person of the same age, status, or ability. In this context, pressure source could refer to the influence of a group of people on an individual, or the collective pressure that a group of people can put on someone.