Common Adjectives:
* terrible (terrible)
* tendre (tender, soft)
* tranquille (tranquil, calm)
* toujours (always)
* total (total)
* tragique (tragic)
* triste (sad)
* typique (typical)
Less Common Adjectives:
* taciturne (taciturn, silent)
* taillé (tailored, cut)
* tangible (tangible)
* tardif (late, tardy)
* téméraire (rash, reckless)
* terriblement (terribly)
* terrible (terrible)
* timide (timid)
* toxique (toxic)
* traditionnel (traditional)
* transparent (transparent)
* tributaire (dependent, tributary)
* trivial (trivial)
* trompeur (deceitful, misleading)
* turbulent (turbulent)
Note: Some of these adjectives can be used as nouns or adverbs as well.
This is not an exhaustive list, but it includes a good variety of common and less common French adjectives starting with the letter "t".