凹凸|おうとつoutotsu[0]heiban (flat)

1. noununevenness; bumpiness; roughness; ruggedness
2. nounimbalance; inequality; unevenness; disparity

• Synonym凸凹でこぼこNeutralSame meaning as 「凹凸」 but kanji reversed and read でこぼこ; common in speech. Also figurative of unevenness or contrast, as in 「でこぼこコンビ」. 「おうとつ」 is more written/technical.
• Antonym平坦へいたんNeutralRefers to flat ground, and figuratively to matters going smoothly, as in 「平坦な道」; the opposite of uneven 「凹凸」.
• Antonym平滑へいかつWrittenDescribes a flat, smooth surface; a written, somewhat technical term. Opposes 「凹凸」 on whether a surface is even.

For an uneven surface, use 「凹凸（おうとつ）」 in writing, as in 「凹凸のある表面」; in speech say 「でこぼこ」. The opposites are 「平坦」 and 「平滑」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 表面ひょうめんが平たいらでないこと。