General Synonyms:
* Kind
* Mild
* Soft
* Tender
* Delicate
* Soothing
* Calm
* Peaceful
* Tranquil
* Easygoing
* Gracious
* Courteous
Synonyms for "gentle" as a manner:
* Considerate
* Thoughtful
* Respectful
* Patient
* Understanding
* Tolerant
Synonyms for "gentle" as a physical quality:
* Soft
* Smooth
* Subtle
* Fine
* Light
Synonyms for "gentle" as a quality of sound or motion:
* Soft
* Low
* Quiet
* Slow
* Easy
* Smooth
More specific synonyms:
* Benign (kind, not harmful)
* Pliant (easily bent or shaped)
* Tractable (easily managed or controlled)
* Amenable (open to suggestions)
* Mild-mannered (not aggressive)
The best synonym for "gentle" will depend on the specific context in which the word is used.