[follow up] {v. phr.}, {informal} 1. To chase or follow closely […]

[fool around] or [mess around] or [play around] or [monkey around] […]

[fool away] or [fritter away] {v.}, {informal} To waste foolishly. * […]

[foot in the door] {n. phr.}, {informal} The first step toward […]

[for a song] {adv. phr.}, {informal} At a low price; for […]

[for crying out loud] {informal} Used as an exclamation to show […]

[for keeps] {adv. phr.} 1. For the winner to keep. * […]

[for one's sake] {adv. phr.}, {informal} Used with different possessive nouns […]

[for real] (1) {adj. phr.}, {informal} Not practice or play; earnest, […]

[for the life of one] {adv.}, {informal} No matter how hard […]