[not the only fish in the sea] {n. phr.} One of […]

[not the only pebble on the beach] {n. phr.} Not the […]

[not the thing] {n. phr.} Not the accepted form of action; […]

[number one] (1) or [Number One] (1) {n. phr.}, {informal} Yourself; […]

[nut] {n.} 1. Head. 2. Eccentric person.

[nut case] {n. phr.} A very silly, crazy, or foolish person. […]

[nutcase] {n.} An insane person.

[nuthouse] {n.} A lunatic asylum.

[nuts and bolts of] {n. phr.} The basic facts or important […]

[nutter] {n.} Insane person.