洽 is a bound form (b.f.) that appears in compound words. Its two main meanings are 'harmonious' (as in 融洽 'harmonious, getting along well') and 'to consult/negotiate' (as in 洽谈 'negotiation, talks'). A less common sense is 'extensive' (as in 洽博 'extensive and learned'). You'll encounter 洽 in formal or written contexts, especially in business and diplomatic language.