Yes, tense is a Scrabble word!

Verb

1. Become stretched or tense or taut

2. Increase the tension on

3. Become tense, nervous, or uneasy

4. Cause to be tense and uneasy or nervous or anxious

Adjective

1. In or of a state of physical or nervous tension

2. Pronounced with relatively tense tongue muscles (e.g., the vowel sound in `beat')

3. Taut or rigid; stretched tight

Noun

1. A grammatical category of verbs used to express distinctions of time