Peakier is the comparative form of peaky, meaning more pale, sickly, or wan in appearance.
Someone who looks peakier than usual appears more unwell or run-down: You're looking peakier than you did yesterday—maybe you should see a doctor.
The word is more common in British English.
1. unwell — pallid, Unhealthily lacking color; wan (Pale and unwell-looking); sallow (Unhealthily yellowish complexion); gaunt (Lean from deprivation); haggard · feverish · queasy · nauseous · fatigued · lethargic · frail · weak · ailing · infirm
2. pointed — spiky, Having sharp projections; jagged (Sharply uneven, notched); sharp (Fine-edged, or astute); angular (Sharp-edged or rawboned); tapered · serrated · craggy · ridged · mountainous · crested · uneven · irregular · spired · pinnacled