skeleton, bone, remains, frame
骨 centers on the hard structural parts of a body: bones and skeletons. It extends naturally to the framework or core of something, and to remains after death.
骨 is a pictograph of a bone or skeleton. The modern form retains a stylized top representing the bone shape and a bottom derived from 肉 (flesh), emphasizing the bodily context.
The top part 冎 looks like a joint or bone structure, and the bottom ⺼ is flesh. Together they show the hard parts inside the body: bones and skeleton.
For コツ, imagine a skeleton that is all hard bits and pieces: the word 'cots' (like 'cots' in 'apricots') sounds like コツ, and the skeleton is made of many small bone bits.
bone
bone fracture
knack; skill; trick; secret; know-how; the ropes; hang
skeleton; skeletal structure; build; frame; physique
pelvis
antique; curio
open; unconcealed; undisguised; blatant; plain; frank
cremated remains (esp. the bones); ashes
spine; backbone; spinal column
skull; cranium
collarbone; clavicle
rib
cartilage
bone marrow; medulla
steel frame; steel beam; steel girder
white (bleached) bone; skeleton
skeleton
boning (fish or meat); deboning
bonesetting
human bones