Common adjectives:
* Tendre (tender)
* Terrible (terrible)
* Trist (sad)
* Tout (all, every)
* Tranquille (calm, peaceful)
* Très (very)
* Tropical (tropical)
Less common adjectives:
* Taciturn (taciturn)
* Tardive (late)
* Teinté (tinted)
* Tempêteux (stormy)
* Tendu (tense)
* Terne (dull)
* Terrible (terrible)
* Tiède (lukewarm)
* Timide (shy)
* Tolérant (tolerant)
* Travers (across)
* Troublé (troubled)
* Turbulent (turbulent)
Note: Some of these adjectives are more commonly used as adverbs (e.g., très) and some might be considered "participles" depending on the context.
This list is not exhaustive, but it provides a good starting point for exploring French adjectives beginning with "T".