noun

1. An only child.

adjective

1. Alone in a category.

   “He is the only doctor for miles.”

2. Singularly superior; the best.

3. Without sibling; without a sibling of the same gender.

   “He is their only son, in fact, an only child.”

Synonyms: lone, sole, nonpareil, peerless, unequaled

adverb

1. Without others or anything further; exclusively.

   “My heart is hers, and hers only.”

2. No more than; just.

   “If there were only one more ticket!”

3. As recently as.

   “He left only moments ago.”

conjunction

1. Under the condition that; but.

   “You're welcome to borrow my bicycle, only please take care of it.”

2. But; except.

   “I would enjoy running, only I have this broken leg.”