AbiWord seems like an odd choice for a word processor— it seems to be virtually obsolete.
Is there anything newer that isn't absurdly bloated?
There's KWrite, but I'd be surprised if that were less bloated than AbiWord.
Markdown text might be fine, but I wouldn't expect markdown to PDF via pandoc to be particuarly "lightweight." There's the range of typesetting or desktop publishing stuff like TeXmacs, groff, or LyX, but I don't expect those to be particularly light, either. There's WordGrinder, a terminal based word processor, but I've never used that.