Yes — "only" is a First Grade sight word. Its "o" makes a long "o" sound in an unusual position, and its frequent use across all kinds of sentences earns it early sight-word status.
There was only one cookie left.
"Only" contains the smaller familiar word "on", which can help a child anchor the spelling, but the shift from short-o in "on" to long-o in "only" isn't obvious from the letters alone. Because it's used so frequently to express limitation or exclusivity, it's practiced as a sight word from an early stage.
Point out that "only" starts with the familiar word "on" — a helpful anchor even though the vowel sound changes in the full word.
Word Wizard teaches "only" with Flash Cards, Listen & Pick, Spell It, and Write It — four game modes that turn repetition into play.
See "only" with its picture, syllables, and example sentence — with native audio.
Hear "only" spoken aloud and pick it out from similar-looking words.
Build "only" letter by letter from shuffled tiles.
Word Wizard turns sight word practice into a game — Flash Cards, Listen & Pick, Spell It and Write It, from Pre-K through Grade 5.