Isogloss

The term isogloss (Ancient Greek ἴσος ísos "equal, similar" and γλῶσσα glōssa "tongue, dialect, language") is inspired by contour lines, or isopleths, such as isobars.

[1] The centum–satem isogloss of the Indo-European language family relates to the different evolution of the dorsal consonants of Proto-Indo-European (PIE).

In the standard reconstruction, three series of dorsals are recognised: In some branches (for example Greek, Italic and Germanic), the palatals merged with the velars: PIE *keup- "tremble (inwardly)" became Latin cupiō "desire" and *ḱm̥tom "hundred" became Latin centum (pronounced [kentum]); but *kʷo- "interrogative pronoun" became quō "how?

In other branches (for example, Balto-Slavic and Indo-Iranian), the labiovelars merged with the velars: PIE *keup- became Vedic Sanskrit kopáyati "shaken" and *kʷo- became Avestan kō "who?

Thus, in Proto-Semitic and subsequent non-Northwest Semitic languages and dialects, the root letters for a word for "child" were w-l-d.

[5] For example, a distinguishing feature of the Iron Age Old Hebrew script is that the letters bet, dalet, ayin and resh do not have an open head, but contemporary Aramaic has open-headed forms.