Decide upon' is a phrase that means to make a choice or come to a conclusion after careful consideration. The crossword solutions for this phrase are ELECT (5 letters), SET (3 letters), and OPT (3 letters). ELECT means to choose by voting, while SET means to put in place or establish. OPT is a verb meaning to choose or select. Therefore, the phrase 'decide upon' can be broken down into three words that mean to choose, establish, and select.