1. (verb) make more subtle or refined

• rarefy
• sublimate

2. (verb) make (senses) more keen

• subtilise

1. (verb) mark fine distinctions and subtleties, as among words

• discriminate
• know apart

2. (verb) make more subtle or refined

• alter
• change
• modify

3. (verb) make (senses) more keen

• heighten
• sharpen