Spring’s opposite, tidally

NEAP

Think of the weaker tides that occur when the sun and moon pull at right angles, twice a month. This term also describes something small or modest.

Spring’s opposite" hints at the opposite of spring tides—the extreme high and low tides caused by the moon and sun aligning. That’s neap tides, which happen when they’re at right angles, creating weaker tides. "Tidally" confirms we’re talking about tides, so the answer is simply NEAP, the short form of neap tide. The clue plays on both the seasonal word "spring" and its tidal meaning.