lucubration

n. 刻苦研究，苦思冥想

lubber, lubberly, lubricant, lubricate, lubrication, lubricious, lucerne, lucid, lucidity, lucidly, luck, luckily, luckless, lucky, lucky dip, lucrative, lucratively, lucrativeness, lucre, Lucretius, Luddite, ludicrous, ludicrously, ludicrousness, ludo, luff, luffa, lug, luge, luggage, luggage-rack, luggage-van, lugger, lugubrious, lugubriously, lugubriousness, lugworm, lukewarm, lull, lullaby,