赤

Matsubara's red rockfish (Sebastes matsubarae)

red river hog (Potamochoerus porcus); bush pig

red letter style; cutesy fashion style named after fashion magazines featuring it (whose cover titles are printed in red or pink)

Colloquial

red sea bream (i.e. the tai, Pagrus major)

Sumo; Food, cooking

fish given to a tournament winner as congratulations

red cabbage

Hanafuda

scoring combination consisting of the January, February and March 5-point cards

facial gesture of pulling one's eyelid down and sticking out one's tongue

Computing

red-black tree; self-balancing binary search tree

Red Crescent Society

brown bear (esp. the Ussuri brown bear, Ursus arctos lasiotus)

Word usually written using kana alone

Matsubara's red rockfish (Sebastes matsubarae)

Food, cooking; Kantou-ben

red rockfish; red scorpionfish

red kidney bean

scalloped hammerhead (Sphyrna lewini); bronze hammerhead shark

equatorial radius

doldrums

red stingray (Dasyatis akajei)

vivid crimson

red soil aggregate; akadama; clay-like volcanic ash soil (used for bonsai, etc.)

whiskered velvet shrimp (Metapenaeopsis barbata); red rice prawn

Colloquial

spider mite (any mite of family Tetranychidae)

Japanese sea fig (Ficus superba var. japonica)

Red Cross Convention

red snow (due to microscopic algae, yellow sand, etc.)

common house mosquito (Culex pipiens); northern house mosquito