Psychol. in emotional equilibrium and responsive to the environment
See syntonic in American Heritage Dictionary 4
syn·ton·ic
adjective
Psychology Characterized by a high degree of emotional responsiveness to the environment.
Electricity Of or relating to two oscillating circuits having the same resonant frequency.
Origin: From Greek suntonos, high-strung, intense, attuned, from sunteinein, to draw tight : sun-, syn- + teinein, to stretch; see ten- in Indo-European roots.