1 SHANNON—Irish river. (flow-er, not flower).
5 DECODE—find the meaning of. "Ode" (poem) added to "DEC."
9 INNOCENT—opposite of "guilty." "O" (zero) "cent" (money) after "inn" (pub).
10 BEACON—guiding light. Literally in "could (be a con)-fused".
12 DEEP END—profound conclusion. "Pen" (writer) jumping into (hint) "deed" (action).
13 EXTREME—ultimate. Literally in "t"(ext reme)dies.
14 EULER—Swiss mathematician. "E" (east, i.e. oriental) plus changed (anagram of) "rule."
16 INTRO—colloquial short form of "introduction," i.e. preamble. Wild (anagram of) "riot" about (around) "N" (compass point).
17 EXTRA—something more. "Ex" ("expert" less four letters of six) plus "tra," i.e. "art" back(ward).
18 APART—separated. A-part (piece).
20 AFRICAN—continental. Maybe (anagram of) "i" (one) "fan car."
21 ANNULAR—ring-shaped, around. Annul (abolish) a (right).
23 RETAIN—keep. "E" and "T" (head and tail of "elephant") in(side) "rain."
24 DISTRESS—heartache. Di’s (Dianna’s) tress (lock of hair).
25 YEMENI—type of Arab. "Men" and "I" after "ye" (half of "year," i.e. six months).
26 ENCASES—surrounds. "Ease" surrounding (double use) "NC" added to "S" (compass point).
1 SWINDLE—something not fair. "Win" in(side) perhaps (anagram of) "sled."
2 ANNIE—noted (musical) lady. Advised to get a gun (arms).
3 NUCLEAR REACTION—powerful reaction (response) from nucleus (heart). Extra hint: "r" (right) taken from "heart" gives "heat."
4 NON-ADDICTING—not habit-forming. Possibly (anagram of) "did on gin can’t."
6 ELECTROMAGNETIC—a (kind of) wave. Generated from charges of the kind (brigade) that produce light (i.e., accelerating electric ones).
7 ORCHESTRA—something that makes harmony. "H" (chemical symbol for hydrogen) in(side) turbulent (anagram of) "star core."
8 ERNIE—man’s name. "N" (head of "Norman") in(side) "Erie" (lake).
11 TEST DATA FILE—experimental results. Reorganized (anagram of) "let’s fit a date."
15 LOGARITHM—type of number. Phonetically similar to "logger" (lumberjack) "rhythm" (music).
19 THRUSTS—urges progress (mechanically, not politically). "H" (initial of "Hoover") in(side) "trust," over (literally) "S" (South).
20 ARRAY—matrix. "Ar" (chemical symbol for argon) plus "ray" (beam).
22 LOESS—geological deposit. "0" (nothing) in(side) "less" (smaller amount).