I found a blessed iron broad spear (-1; 1d8+3 piercing) {x2, 5%} and an uncursed steel scimitar (+3; 1d8+0 slashing) {x2, 5%} going through a dungeon, and since I wasn't sure if the spear was 1h (one handed) or 2h (two handed), I tried equipping both the spear and the scimitar. I was able to do so, and since then, it appears that I've been swinging with both weapons (i have trained two weapon fighting several levels). I consider a 2h weapon to be exclusively so, regardless of skills. Perhaps a particularly strong person could wield a two handed weapon in one hand, but I only have 16 strength.