fit, suit, join, 0.1
合 centers on things coming together to form a matching whole: fitting, suiting, or joining. The numeric sense '0.1' is a specialized unit of volume derived from the idea of a combined measure.
case; occasion; situation; circumstances
to come together; to merge; to unite; to meet
match; game; bout; contest
gō; traditional unit of volume, approx. 180 ml
synthesis; combination; integration; putting together
circumstances; condition; convenience
combination; assortment; set
acquaintance
passing (an exam); pass; success; passing grade
to be in time (for)
condition; state
sum total; total amount
meeting up; gathering; assembly
union; combination; alliance; confederation; coalition
association; socializing; socialising; fellowship
association; union; guild
(coming to an) agreement; consent; mutual understanding; accord; consensus
integration; unification; unity; combination; consolidation; synthesis
rate; ratio; percentage; proportion
composition; synthesis; compounding; combining
inquiry; query; enquiry
rationality
agglutination; adhesion; fusion; combination; blending; uniting
to match (rhythm, speed, etc.)
合 combines 亼 (an inverted mouth or a lid) and 口 (mouth), suggesting a lid fitting onto a container or two mouths meeting in agreement. The idea of joining or fitting together is well established.
The top 亼 looks like a lid, and the bottom 口 is an opening. Picture a lid fitting perfectly onto a container: 合 means fit, suit, or join.
For ゴウ, imagine a go-between joining two parts: go -> ゴウ, and the go-between makes everything fit together.