Formerly, upper element was「many filled muck orifices」(疊, tripled) then simplified to「plugged orifice with stickiness」「surrounding and piled」meaning LAYERS, and REPEATED, PILED ON TOP OF OTHERS, FOLDED. Perhaps a place where many filled orifices (or, human backsides) could sit together on FOLDED MATS, and in very humid weather one's backside might not sweat as much while sitting. The Chinese glyph from which this is derived does not refer to tatami or matting at all—the word 'tatami' and its meaning were added by the Japanese many centuries later, so this glyph must have meant something else originally. The outside surfaces of tatami mats are not woven from rice straw (too brittle, too short) but rather, from split igusa reeds. Rice straw was bundled and simply packed within the woven reeds. Top element is「wetlands」(where the reeds can be found) or「filled orifice.」Older glyphs all with the same meaning include「many crotches accumulated」and「alternating between plugged orifices」that「surround on all sides and are accumulating.」Also meaning REPEATED USE, REPEATED ACTION, BENT OVER and ACCUMULATED, LAYERED. USING MATS necessary for sexual activity would certainly make everything more pleasant. Nevertheless, some still claim that the top element as「rice paddy」is an oblique reference to growing rice plants, and growing rice plants as an oblique reference to harvested rice as an oblique reference to the residual straw by-product, a material that was purportedly used for stuffing, plugging TATAMI MATS. They say the meaning of FOLDED derives from the construction method of REPEATEDLY folding woven single layers of rice straw into thicker layers, and finally「surrounding」the thickly folded,「piled up」layers into a TATAMI mat, none of which is the actual production method of tatami.

Modern definitions (that generally disregard history) …excluding politically incorrect concepts and other meanings deemed offensive today; may list only pigeonholed definitions, euphemisms, or meaningless mnemonics)
Unihan extended: repeat, duplicate; repetitious
EDRDG: counter for tatami mats; fold