• 許可きょか — permission, approval
• 許容きょよう — tolerance, acceptance
• 免許めんきょ — license
• 特許とっきょ — patent
• 許ゆるす — to allow, to forgive

許 is a 形声文字 (semantic-phonetic compound). The 言 (speech) radical shows it's related to speaking or expressing, and the phonetic part 午 suggests the sound. The character expresses giving permission through speech — hence “allow,” “permit,” and “forgive.”

先生せんせいは 遅刻ちこくを 許ゆるしてくれました。
The teacher forgave the tardiness.

政府せいふは 輸出ゆしゅつを 許可きょかしました。
The government approved the export.

許 is mainly read as キョ in compound words, and ゆるす when used independently in its kun-yomi. Both are frequent and practical in daily life.