"sicklier" in the adjective sense
1. sallow, sickly
unhealthy looking
2. ailing, indisposed, peaked, poorly, sickly, unwell, under the weather, seedy
somewhat ill or prone to illness
"my poor ailing grandmother"
"feeling a bit indisposed today"
"you look a little peaked"
"feeling poorly"
"a sickly child"
"is unwell and can't come to work"
Source: WordNet® (An amazing lexical database of English)
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