The suffix -less attaches to the end of words to mean “without” or “lacking.” When you add it to a noun, you create an adjective describing the absence of that thing.

Think about fearless: someone without fear. Or countless: so many you can't count them, or effectively without number. A wireless device works without wires. A cloudless sky has no clouds. When someone acts in a thoughtless way, they're behaving without thinking about consequences or other people's feelings.

You can spot -less working in dozens of common words: hopeless, helpless, harmless, priceless, restless, endless, timeless. Each time, it usually transforms a noun into an adjective by indicating the absence of whatever that noun represents.

Here's something interesting: priceless doesn't mean worthless (without value). It means so valuable that no price could capture its worth, or without the ability to set a price on it. The Mona Lisa is priceless. Your family photos might be priceless to you.

Understanding -less helps you decode unfamiliar words. If you see fathomless, you can figure out it means impossible to fathom (measure the depth of), or basically without depth. The suffix turns vocabulary into a puzzle you already know how to solve.