Synonyms for Groovy:

adj.

cool, wonderful (adjective)
neat, nifty, sensational, fantastic, swell, great, super, fabulous, splendid.
excellent (adjective)
super.
far-out (adjective)
modernistic, sensational.
fashionable (adjective)
stylish.

n.

futuristic, up-to-the-minute, divine, hot, modernistic, ahead of your/its etc. time, fantastical, fabulous, splendid, tremendous, sensational, terrific, fantastic, contemporary, space age, glorious, cool, superb, wonderful, ripping, state of the art, advanced, modern, dreamy, out of this world, marvelous, super. groovy (noun)
good, cracking, bully, peachy, nifty, smashing, swagger, not bad, great, slap-up, stylish, keen, dandy, swell, corking, fashionable, bang up, neat.

Other synonyms:

ripping. marvelous, tremendous. fabulous, dreamy, wonderful, sensational. glorious. hot, splendid, terrific, cool, divine. fantastical. fantastic. bang-up
bang up.