/makˈsilə/
Noun, pl. maxillae
1. A fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible (lower jaw), which is also a fusion of two halves at the mandibular symphysis. Sometimes (e.g. in bony fish), the maxilla is called “upper maxilla,” with the mandible being the “lower maxilla.” Conversely, in birds the upper jaw is often called “upper mandible.” (wikipedia.org)
2. The upper jaw bone; takes part in the formation of the orbit, hard palate and nasal cavity. (biology-online.org)
3. Either of two membrane bone elements of the upper jaw that lie lateral to the premaxillae and that in higher vertebrates including humans bear most of the teeth (merriam-webster.com); an upper jaw especially of humans or other mammals in which the bony elements are closely fused. (merriam-webster.com)
3. Either of the two bones that together form the upper jaw. (wiktionary.org)
4. Arachnid mouthpart (wiktionary.org); one of the first or second pair of mouthparts posterior to the mandibles in insects, myriopods, crustaceans and closely related arthropods. (merriam-webster.com)
Word origin: From Latin maxilla “upper jaw,” diminutive of mala “jaw, cheekbone.” “Maxilla stands to mala as axilla, ‘armpit,’ stands to ala ‘wing'”