The word 呼叫 is formed by combining two individual characters, each with closely related meanings, to create a stronger, more specific concept. The first character, 呼, depicts a mouth (口) with exhaled breath, conveying the idea of "to exhale" or "to call out". The second character, 叫, also incorporates a mouth (口) component and specifically means "to shout" or "to cry". When placed together, their meanings blend and reinforce one another, visually and semantically merging the act of using one's voice with directed force, resulting in the composite meaning of "to shout for" or "to call out to", as in making a vocal summons or transmission.