Yes, ace is a Scrabble word!

Verb

1. Succeed at easily

2. Score an ace against

3. Play (a hole) in one stroke

4. Serve an ace against (someone)

Adjective

1. Of the highest quality

Noun

1. The smallest whole number or a numeral representing this number

2. One of four playing cards in a deck having a single pip on its face

3. Someone who is dazzlingly skilled in any field

4. Proteolytic enzyme that converts angiotensin I into angiotensin II

5. A major strategic headquarters of NATO; safeguards an area extending from Norway to Turkey

6. A serve that the receiver is unable to reach