She didn’t attend the meeting, for she was feeling unwell. Here 'for' is used as -

• She didn’t attend the meeting, for she was feeling unwell. Here 'for' is used as - Conjunction.

• For (conjunction) 
- (কথ্য ইংরেজিতে বিরল, বাক্যের শুরুতে ব্যবহৃত হয় না) কেননা; যেহেতু; বলে।
- As a conjunction, "for" connects clauses and explains reasons or causes.
- He couldn’t buy the house, for he had no money.

• For (Preposition) 
- উদ্দেশে; অভিমুখে; লক্ষ্যে; দিকে, জন্য; ইত্যাদি অর্থে।
- As a preposition, "for" shows relationships related to purpose, benefit, or intended recipient.
- She worked hard for her success.